Acre (ac)
The acre, or ac, is a unit of area used in the imperial and US systems. It originated in medieval England and referred to the land a team of oxen could plow in a day. Today, one acre is 4,840 square yards or 4,046.856 square meters. Acres are still used in the US, Canada, and the UK for real estate, land sales, and farms. While the metric system is more common worldwide, the acre is still used because it is part of tradition and is easier to use in daily life.
Hectare (ha)
The hectare, or ha, is a metric area unit equal to 10,000 square meters (a square with 100-meter sides). First used in France in 1795, it is now widely used worldwide, particularly in farming, forestry, and land planning. Although it is not an official SI unit, it is permitted because it is practical for measuring fields and properties. Its simple size makes it better than the square kilometer for medium areas.